Yes as BA Silver you can access any oneworld Business Class lounge globally (QR lounges and QF Domestic Business are exceptions) irrespective of route or class of travel. I suspect your confusion might’ve arisen from the lounge access rules when travelling domestically in the US, again these don’t affect you as a BA status holder. So enjoy All you ever need is a oneworld marketed and operated ticket with your BAEC number inserted in the booking and you’re good to go, along with one guest (provided they’re travelling on a oneworld marketed and operated ticket also)